Hydraulic drive system for forging press or forging machine slides

ABSTRACT

The invention relates to a hydraulic drive system for the tool-bearing slide of a forging press or a forging machine. The slide is configured as a piston and is provided with a valve seat at the opposite end of the tool, that is, the end which is impinged upon by pressure means. Together with a valve lifter driven by an actuator, said valve seat forms a valve which is able to connect the cylinder chamber to a pressureless discharge pipe and therefore control the stroke of the piston. In order to reduce the mass and the axial construction length of the inventive drive system, the piston is hollow over a portion of its length from the end which is impinged upon, and is provided with the valve seat at the base of the hollow. The valve lifter, which can be axially displaced in the cylinder lid, is tubular in shape and is provided with side channels connecting its inner cavity to a pressureless discharge pipe for the pressure means.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT/DE98/02975 filed Oct. 8,1998 and is based upon German national application 197 45 505.0 filedOct. 15, 1997 under the International Convention.

FIELD OF THE INVENTION

The invention relates to a hydraulic drive for slides of amultiple-slide forging machines as known from DE-C2 38 03 632.

BACKGROUND OF THE INVENTION

The slides of such a forging machine, each bearing a tool, are built aspistons which, at their end opposite to the tool acted upon by apressure medium, are provided with a valve seat connected to a centralthroughflow bore, which via side channels is connected to a chamber keptpressureless by means of a discharge line. A valve lifter controlled byan actuator cooperates with the valve seat on the piston and controlsthe piston stroke. The pistons are designed as differential pistons andare constantly acted upon by the pressure medium at their piston ringsurface in the pull-back direction. This drive system is characterizedby its good dynamics and simple construction.

Because of its good dynamics, this drive system is well suited for usein high-speed forging presses, which as a replacement of forginghammers, should reach 180 to 240 strokes per minute. The problem here isthat forging presses have to be laid out for substantially biggerstrokes than the relatively short-stroke forging machines, whereby theaxial length of the drive system and the slide mass increasecorrespondingly.

OBJECT OF THE INVENTION

It is the object of the invention to improve the drive system known fromDE-C2 38 03 632 rendering it applicable to high-speed forging presses.

SUMMARY OF THE INVENTION

In order to solve this problem a reduction of the axial length of thedrive system with the reduction of its mass is targeted, which isachieved by making the piston partially hollow starting from its endopposed to the tool. On the bottom of the hollow is the valve seat. Thevalve lifter is tubular in shape and guided so as to be axiallydisplaceable in the cylinder lid and is provided with side channels inthe cylinder lid connecting the inner space of the valve lifter with achamber surrounding the valve lifter kept without pressure via adischarge line.

In order to achieve this object of the invention aimed at the reductionof the axial length of the drive system, according to another feature ofthe invention, it is further developed in an embodiment in which thedifferential piston step is eliminated.

The piston is built as a plunger piston which at its tool end isconnected with a tool-bearing upper plate/front plate, which by means ofguide rods is guided in the traverse. The return stroke of the plungerpiston is performed by means of the piston-cylinder units supported inthe traverse.

Four guide rods are preferably provided which are connected in pairsabove the traverse by yoke pieces and between the same and the traversethe piston-cylinder units are arranged for the pull-back.

During the forging operations the pull-back pistons are constantly actedupon from an accumulator to keep them inactive.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 is a perspective view of a forging press, partially sectioned;

FIG. 2 is a cutout during the work stroke;

FIG. 3 is the same cutout during the return stroke;

FIG. 4 is an elevational view of a forging machine, partially insection.

SPECIFIC DESCRIPTION

The forging press consists of a stationary lower traverse 1, an uppertraverse 2 which is also stationary and the columns 3 connecting thesame. The traverse 1 carries a lower saddle 4 opposed by an upper saddle5. The upper saddle 5 is moved by a piston 6 connected to an upper plate7 to which the upper saddle 5 is fastened. A cylinder 8 guiding thepiston 6 is securely mounted in the upper traverse 2 and provided with abushing 9 for the guidance of the piston 6. For the work stroke thepiston 6 is actuatable in the cylinder 8 by a pressure-medium supplyline 10 in the cylinder lid 11. The cylinder 8 and the cylinder lid 11are connected with the upper traverse 2 by means of traction anchors 27.For the return stroke, pull-back cylinders 12 with plunger pistons 13are provided, whereby the retraction or pull-back cylinders 12 aresupported in the upper traverse 2 and the plunger pistons 13 act againstyokes 15. Preferably the plunger pistons 13 in the retraction orpull-back cylinders 12 are constantly acted upon from a low-pressuretank not shown in the drawing.

In a variation of the embodiment shown, piston-cylinder units can beprovided for the pull-back, whose cylinders are fastened in the uppertraverse 2 and from whose piston rods the upper plate 7 is suspended.Also instead of the retraction cylinder, a construction of the piston 6and the cylinder 8 as a double-action piston-cylinder unit can beprovided, whereby the ring surface on piston 6 provided for the pullbackis then constantly actuated.

For the guidance of the upper plate 7, the same is provided with guiderods 14, which at their free ends are connected by yokes 15 and areguided by bushings 16 in the upper traverse 2. For the pressure mediumsubjected to pressureless discharged during standstill and pullback, adischarge line 17 is provided in the cylinder lid 11.

The press stroke is controlled by a valve lifter 18 which cooperateswith a seat surface 19 on the bottom of the partially hollow piston 6.The valve lifter 18 is guided in a hollow pin 21. The valve lifter 18 ishollow and provided with side channels 25 for the pressureless medium atits head end 24 designed for the connection with rod 23. Apiston-cylinder unit 26 is provided as a member of a servocontrol andconnected elastically bendable via the rod 23 with the valve lifter 18.

For the work stroke the valve lifter 18 is pressed down by thepiston-cylinder unit 26 onto the valve seat 19, whereby the piston 6 andthe valve lifter 18 travels together during the downward stroke. Whenthe desired forge dimension is reached, the piston of thepiston-cylinder unit 26 is reversed, i.e. actuated upwards via theservocontrol, whereby the valve lifter 18 moves away from the valve seat19. Through this opening of the valve the work pressure over piston 6 isreduced, in that the pressure medium is discharged through the hollowlifter 18, the side channels 25 in the head 24 of the valve lifter 18and finally through the discharge line 17, so that the piston 6 comes toa standstill after the decompression of the pressure medium. At afurther opening of the valve, the upper forging tool with the upperplate 7 and the piston 6 is lifted by the plunger piston 13 of theretraction cylinders 12 by means of the yokes 15 and the guide rods 14.

The forging machine shown in FIG. 4 has four forging tools arranged inone plane in an X-shape. It consists of a frame 40, composed ofintermediate pieces 41 and traverses 42, interconnected by tractionanchors 43. In each of the four traverses 42 there is a piston 46serving as a slide, provided with a front plate 47, a not illustratedtool being releasably connected with the same. Each piston 46 is guidedin a cylinder 48 which is inserted in its traverse 42. For the workstroke, each piston 46 can be actuated in its cylinder 48 via apressure-medium supply line 50 in the cylinder lid 51. In each instancea cylinder 48, a cylinder lid 51 and a traverse 42 are connected bytraction anchors 67. For the return stroke, retraction cylinders 52 withplunger pistons 53 are provided, whereby the retraction cylinder 52 issupported in the traverses 42 and the plunger pistons 53 act against theyokes 55, which are connected via guide rods 54 with the front plate 47of the pertaining piston 46. The plunger pistons 53 are constantlyactuated in the retraction cylinders 52 via pressure-medium supply lines62 from a not illustrated low-pressure storage tank. For the pressuremedium discharged without pressure during the return stroke andstandstill of the pistons 46, a discharge line 47 is provided in thecylinder lid 51.

For their guidance the front plates 47 are provided with guide rods 54.which at their free ends are connected with the yokes 55 and are guidedby bushings 56 in the pertaining traverse 42.

The stroke of the pistons 46 is controlled by valve lifters 58, whichcooperate with seat surfaces 59 on the bottoms 60 of the pistons 46which are hollow over a portion of their length. Each valve lifter 58 isguided in a hollow pivot 61 connected with the cylinder lid 51 of thepertaining cylinder 48. The valve lifters 58 are hollow and providedwith side channels 65 for the pressureless pressure medium at their headend 64 designed for the connection with the rods 63. Each valve lifter58 is connected elastically bendable via rods 63 with a piston-cylinderunit 66 as member of a servocontrol. For the work stroke the valvelifters 58 are pressed down onto their valve seats 59 by the pistons ofthe piston-cylinder units 66, whereby the pistons 46 and the valvelifters 58 travel together over the stroke path. When thecontrol-determined stroke path has been completed, through theservocontrol the piston of the piston-cylinder unit 66 is acted upon inthe opposite direction, whereby the pertaining valve lifter 58 is movedaway from its valve seat 59. Due to this opening of the valve formed bythe valve lifter 58 and the valve seat 59, the work pressure is reducedover the respective piston 46, in that the pressure medium is dischargedvia the hollow valve lifter 58 and the side channels 65 in the head end64 and finally through the discharge line 57, so that the piston 46comes to a standstill after the decompression of the pressure medium. Ata further opening of the valves, the pistons 46 are moved in returnstroke by the plunger pistons 53 over the yokes 55, the guide rods 54and the front plate 47 into their initial starting positionpredetermined by the position of the valve lifters 58.

We claim:
 1. A forging apparatus comprising: a support; at least onetool-bearing slide on said support formed with a piston having a closedend provided with a forging tool and at least partially hollow and opentoward an opposite end of said piston; a cylinder on said support inwhich said piston is guided, said cylinder having a cylinder lid at saidopposite end of said piston, said cylinder lid being provided with apassage delivering a hydraulic medium to said cylinder and an interiorof said piston, and with an outlet for said hydraulic medium; a valveseat formed in said piston; an axially displaceable tubular valve lifterguided on said cylinder lid, extending into said piston and engageablewith said valve seat, said valve lifter forming with said valve seat avalve closing communication between said cylinder and said outlet, saidvalve lifter being provided with side channels in said cylinder lid forconnection with a chamber surrounding said valve lifter andcommunicating with said outlet, said valve lifter controlling flowbetween said passage and said outlet, said chamber being maintainedwithout pressure by said outlet; and an actuator connected with saidvalve lifter for operating same.
 2. A forging apparatus comprising: asupport; at least one tool-bearing slide on said support formed with apiston having a closed end provided with a forging tool and at leastpartially hollow and open toward an opposite end of said piston; acylinder on said support in which said piston is guided, said cylinderhaving a cylinder lid at said opposite end of said piston, said cylinderlid being provided with a passage delivering a hydraulic medium to saidcylinder and an interior of said piston, and with an outlet for saidhydraulic medium; a valve seat formed in said piston; an axiallydisplaceable tubular valve lifter guided on said cylinder lid, extendinginto said piston and engageable with said valve seat, said valve lifterforming with said valve seat a valve closing communication between saidcylinder and said outlet, said valve lifter being provided with sidechannels in said cylinder lid for connection with a chamber surroundingsaid valve lifter and communicating with said outlet, said valve liftercontrolling flow between said passage and said outlet, said chamberbeing maintained without pressure by said outlet; an actuator connectedwith said valve lifter for operating same, the piston being a plungerpiston formed at said closed end with a tool-bearing upper plate; andguide rods guiding said upper plate on said support and further pistonson said support and acting upon said guide rods for pulling back saidupper plate upon displacement of said tool-bearing slide in a forgingoperation.
 3. The forging apparatus defined in claim 2 wherein saidsupport includes an upper traverse provided with four of said guide rodsconnected in pairs above said traverse by respective yoke pieces, thepistons for pullback of said plate being braced between said yoke piecesand said traverse.
 4. The forging apparatus defined in claim 3 whereinthe pullback pistons are constantly acted upon by said hydraulic mediumfrom an accumulator to maintain them inactive during forging operations.